Soap builder of reduced alkalinity



or sodium silicate, used Patented Sept. 21, 1937 PATENT OFFICE SOAPBUILDER or nan'ucrn ALKALINITY Walter C. Preston, The Procter &

Gam

Cincinnati, Ohio, assixnor to ble Company, Cincinnati,

Ohio, a corporation of Ohio No Drawing. Application May 8, 1935,

Serial No. 20,423

9 Claims.

This invention relates to an eillclent soap builder having alkalinitynotsubstantiallygreater than that of soap, solutions, consisting of a saltor salts of pyrophosphoric acid.

The word builder" is used herein with the meaning given in Webster's"New International Dictionary of the English Language, second edition,1935: A substance, as soda ash, caustic soda, with or insoap, to aid incleansing. Most soap builders improve not only the cleansing power butalso the sudsing power of soap, both in soft water and in hard water,and in addition they are capable of softening hard water.

The builders commonly used in laundry soaps, such as sodium carbonate,sodium silicate, and trisodium phosphate, are stronger in alkalinitythansoap itself when measured at the usual concentrations andtemperatures of soap usage. They owe their effectiveness as builderspartly to their ability to combine with. the constituents present innatural hard water and form precipitates with.them, thus avoiding theloss of a certain amount of soap which would otherwise be used up inprecipitating these same constituents. It should be borne in mind that,in general, ordinary soap will "not produce a noticeable lather or exertuseful detergent effects in hard water until the hardness (orsoap-precipitating) constituents of same have first been precipitated orneutralized in some way.

The alkalinity of soap itself when dissolved in water has been reportedby various observers to be about 9 to 10 on the pH scale. Ordinary soapbuilders, however, when added to soap. in suflicient quantities to beeffective as soap builders, unavoidably raise the alkalinity to a pointwhich causes such undesirable effects as irritation of the skin, injuryto woolens and other delicate fibers, deterioration of colors, etc.

I have found that a very effective soap builder, which can be readilyadjusted in alkalinity so that it is mild in its action on the skin, onfabrics, dyes, etc., without losing its great efficlency as an aid incleansing, can be prepared from tetrasodium pyrophosphate.

Tetrasodium pyrophosphate by itself has already been suggested as a soapbuilder, but it has an alkalinity in dilute solution nearly as great asthat of sodium carbonate. However, by treating the tetrasodiumpyrophosphate with suitable small quantities of an acid such as sulfuricacid, hydrochloric acid, phosphoric acid, pyrophosphoric acid, aceticacid, higher fatty acids such as lauric and oleic, etc., or with acidsalts such cated, is peculiar to this as sodium hydrogen sulfate, sodiumdihydrogen phosphate, disodlum dihydrogen' pyrophosphate (NazHzPzOv),and similar acid reacting materials, the normal tetrasodiuinpyrophosphate may be transformed in part into an alkali metalhydrogensalt, and the alkalinity of the tetrasodium pyrophosphate can thus bereduced and adjusted within a widerange. For use as a soap builder,however, the alkalinity should not be reduced substantially below thatof soap itself under similar conditions such as concentrations of 0.5per cent and at room temperature. My discovery is that when thealkalinity of the tetrasodium pyrophosphate is thus reduced to any pointbetween that of the original salt and that of a soap as measured in theusual concentrations of use, such as 0.5 per cent, the efliciency of thepractically unimpaired,

soap builder remains while its alkalinity and effect on the skin, etc.,can be adjusted to any desired degree. Hence, my builder can be used inany desired proportions so as to make soaps suitable for use in any kindof service, while the alkalinity can be regulated so that the soap willbe mild in its action on the hands, fabrics and colors. This, therefore,enables adjustment by the soap maker of his formulas to meet therequirements of various cleansing processes and for varying degrees ofwater hardness such as occur in difierent sections of the country. I

This property of my pyrophosphate builder, of retaining its efliciencyas a soap builder practically undiminished when its alkalinity isreduced even as low as that of soap by the means indisubstance alone, asfar as I am aware. If one attempts to reduce the alkalinity of othercommon soap builders such as sodium carbonate, sodium silicate, ortrisodium phosphate, for example, in a similar way,'their efiiciency assoap builders is markedly decreased.

.My builder softens water in a manner quite different from sodiumcarbonate, orthophosphate, silicate and similar water SOftBl'lElSpWhiChform precipitates with the lime and magnesium, etc., in the water. Thereaction of pyrophosphate salts with the calcium, magnesium, iron andother mineral salts present in hard water, in the presence of a suitableexcess of the pyrophosphate, is thought to proceed as represented by thefollowing chemical equations:

whether the solution The calcium (also magnesium, iron, etc.) behaves asthough it were sequestered in a complex ion, '(CaPzOq), and theconcentration of free calcium (magnesium, etc.) ions in the solution isthus negligible when a sufllciently large excess of pyrophosphate ispresent. Thus, the calcium, magnesium, iron, etc., remain in solution,but in a form not precipitable by soap when suiiicient pyrophosphate ispresent, and water softening is nevertheless complete, the process notbeing accompanied by any precipitation.

Other alkali metal pyrophosphate salts such as the potassium salt can beused in place of the sodium salts, but throughout this specification thesodium salt will be spoken of as representative of all.

While any of the means previously mentioned may be used to reduce thealkalinity of tetrasodium pyrophosphate in the practice of my invention,I find that one of the most convenient is.

to add to the normal NarPzOv some NazHzPzO'z, or any alkalimetal-hydrogen salt of pyrophosphoric acid of the general formulaMrH4-:P20'l, where M is an alkali metal and a: is any positive numericalvalue less than 4.

Solutions of NazHzPzOw are sufficiently acid to turn methyl orangeindicator pink, while solutions of NarPzO'z are alkaline tophenolphthalein as well as methyl orange and have a pH value slightlyless than that of NazCOa. these two salts of pyrophosphoric acid in theproper proportions, any degree of alkalinity or pH value lying betweenthese two extremes can be obtained. 7

In preparing suitable mixtures of these salts, or in reducing thealkalinity of Na4PzO'1 by any other means, it is undesirable to reducethe alkalinity appreciablyv below the alkalinity of soap itself, and forthe purpose of controlling such mixtures various means may be used. Thedetermination of the pH of soap solutions is rather difficult andsubject to considerable error; hence, this is not an easily carried outprocedure. For practical purposes, however, indicators may be used totest solutions which have been prepared with the desired concentrationand these will indicate with sufiicient accuracy by the color of builderis more or less alkaline than the solution of soap. Another methodconsists in adding the mixture of pyrophosphate salts to-a soap solutionand observing whether an increased cloudiness results, or not. Anyincreased cloudiness in solutions having the concentrations of soap andbuilder as ordinarily used in laundering would indicate too low a degreeof alkalinity of the pyrophosphate salt mixture. I

My invention, as previously explained, is not limited topyrophosphatebuilders of an alkalinity equal to that of soap. Itincludes also any pyrophosphate builders of an alkalinity less than thatof tetrasodium pyrophosphate, but not substantially less than that ofsoap. The exact degree of alkalinity that can be tolerated in thebuilder is dependent upon the use to which the built product is to beput. In general, mixtures containing more than one part by weight ofNa2H2P2O7 to four, parts by weight of Na4PzO1 in solution have too low apH value to come within the scope of my invention, while mixturescontaining less than one part of NazHzPzO'l to four parts of NalPzO-lcome within its scope. It will be noted, therefore, that mixturescontaining Na2H2P2O'1 and NarPzOw in the proportion of 1 to 4 by weightwill have the. following apparts of Na4P2O7 By mixing salt being reducedto proximate apparent formula: Na3.54Ho.4sP201. Thus, in general, themixtures coming within the scope of my invention have an average generalformula of Main-E201 where M represents an alkali metal and a: is anyvalue less than 4 but not less than about 3.54.

In the majority of cases, I prefer to use from per cent to per centNaaPzOv and from 5 per cent to 10 percent NazHzPzO'z, such mixturesbeing most widely applicable. The approximate apparent formulas for the9040 and 95-5 mixtures are Naan'zHoaaPzO'i and Na3.saHo.izP20'z,respectively.

As an example of my invention, I mix nine with one part of NazHzPzOi. Ithen add two parts of this mixture to eight parts of powdered soda soapmade from beef tallow. The resulting built soap is of a mildness similarto that of unbuilt tallow soap and affects indicators in a similarmanner. When, under practical washing conditions, thebuilt soap wascompared with the unbuilt soap at F. in equal concentrations in water ofseven grains hardness per U. S. gallon, it was found that the built soapequaled the unbuilt taliow soap in sudsing power and excelled it in theremoval of an oily type of soil from cloth. It will thus be seen thatthe builder replaced its own weight of soap as measured by sudsing powerand more than its own weight of soap as measured by detergent power.When the comparison was made between built and unbuilt soap solutionshaving equal real soap concentrations, then an improvement in bothsudsing and detergency was noted.

Other soaps than tallow soap, for example, coconut oil soap, palm kerneloil soap, palm oil soap and various mixtures of same may be improved inboth sudsing and detergent power by the addition of my builder.Likewise, other alkali metal soaps such as the potassium soaps may besimilarly improved, in which case, it may be advantageous to use thecorresponding alkali metal pyrophosphate salts as builder.

My invention is not limited, however, to any particular method of mixingthe pyrophosphate salts with the soap. Pyrophosphate salts of reducedalkalinity may be incorporated into soap in any of the forms in whichsoap in manufactured, as milled or unmilled bars, as flakes, powder,gel, or solution. It'may be mechanically mixed in, as in the aboveexample; it may be crutched into the molten soap; it may be dissolved ina soap gel or solution. In certain methods involving saponification inthe crutcher, it is feasible to conduct the saponification with amixture of tetrasodium pyrophosphate and caustic alkali, the alkalinityof the pyrophosphate the desired point by the addition of fatty acidtoward the end of the reaction,

While such a ready-for-use mixture may be manufactured and is for manypurposes preferable, it also lies within the scope of my invention toadd my builder to water prior to adding soap, or vice versa, or to addboth builder and soap simultaneously but separately to the water. Myinvention resides in the presence in the detergent solution at thetimeof use, of soap and ously with solution in the wash water. My 75 watersoftening, sudsing, and detergent propera value less than 4 but not lessthan about 3.54.

builder may, however, be used in conjunction with other known soapbuilders if'so desired.

Throughout the specification I have referred to the anhydrouspyrophosphate salts in the description of my invention. However, it isunderstood that I do not exclude from its scope those builders preparedfrom corresponding hydrated salts.

The word soap as used in this specification and claims means awater-soluble soap suitable for detergent purposes.

Having now described my invention, what I claim and desire to secure byLetters Patent is: 1. A soap builder having substantially the samealkalinity as soap alone under similar conditions of use, and adapted toimprove the water softening, sudsing and detergent properties ofwatersoluble soap, comprising essentially an alkali metal pyrophosphateof reduced alkalinity hav-' ing the general average formula MeH4-zP2O7wherein M represents an alkali metal and a: has a value less than 4 butnot less than 3.54.

2. A soapbuilder suitable for improving the water softening, sudsing anddetergent properties of soap, and suitable for use with soap'in anyproportion needed for varying cleansing requirements and for water ofvarious degrees of hardness without increasing the alkalinity of thesoap product beyond-a predetermined low point, consisting of atetra-alkali-metal pyrophosphate with an alkali-metal-hydrogenpyrophosphate, said mixture having the general averase formulaM:H4-:P207

wherein M represents an alkali metal and a: has any value less than 4'but not less than about 3.54, the proportions of the .two pyrophosphatesbeing selected within this range so as to give the desired lowalkalinity to the product.

' 3. A soap builder, efliciert in water softening and in improving thesudsing and cleansing power of soap without substantially increasing thealkalinity of the soap, consisting essentially of a mix-.- ture of about90 parts by weight of tetra-sodium pyrophosphate and about 10 parts byweight of disodium-dihydrogen pyrophosphate.

4. A soap builder, suitable for improving the ties ofwater-soluble soapwithout increasing the alkalinity of the soap. which comprises a mixtureof a tetra-alkali-metal pyrophosphate and 55 an alkali-metal-hydrogenpyrophosphate, said mixture having substantially the same alkalinity asthe soap and having the following general average formula M:;H4-:P2 01wherein M represents an alkali metal and a: has

5. As-a new washing composition, water-soluble soap anda builder forsame consisting essentially of tetra-alkali-metal pyrophosphate andalkali-metal-hydrogen pyrophosphate in suitable proportion so that saidbuilder has the general average formula MzH4-a-P207 wherein M representsan alkali metal and :vhas any value less than 4 but not less than about3.54.

6. As a new washing composition, water-soluble soap and a builder forsame consisting of a mixture of about 90 parts by weight of tetra sodiumpyrophosphate and about 10 parts by weight of disodium-dihydrogenpyrophosphate. '7. As a new washing composition, water-'solu ble soapand a builder for same consisting essentially of tetra-alkali-metalpyrophosphate and a sufllcient proportion of a compound selected fromthe group consisting of acids and acid reacting salts such that said ageformula builder has the general averl MJIr-ePiOi wherein M represents analkali metal and a: has a value less than 4 but not less than 3.54.

9. A-soap builder suitable for improving the water softening, sudsingand detergent properties of water-soluble soap and suitable 'for usewith water-soluble soap in any proportion needed for varying cleansingrequirements and for water of various degrees of hardness withoutincreasing the alkalinity of the soap product beyond a predetermined lowpoint, comprising a mixture of tetra-alkali-metal pyrophosphate with'asumcient proportion of a compound selected from the group consisting ofacids and acid reacting salts, to reduce the alkalinity of the saidpyrophosphateso that it will have the general average formula .wherein Mrepresents an alkali metal and has this range so as to give the

